The invention relates to liquid volume measurement and more particularly to a dip stick for measuring the amount of liquid in a deep container such as a gasoline storage tank.
Service station gasoline and diesel fuel storage tanks are normally set underground and are over 10 feet deep. In order to measure the amount of liquid in the tank at any time, a long stick-like structure may be inserted down from the top of the tank and then removed and examined. Conventional dip sticks in current use are constructed entirely of a solid strip of wood which shows discoloration or wetness for some period of time over that portion of the stick which has been submerged in the liquid. The stick is normally calibrated so that the height of the liquid may be accurately determined at the boundary of wetness to dryness as indicated by the temporary discoloration. A conversion table is used to determine the quantity of liquid in the tank for the determined height.
Conventional dip sticks have a number of disadvantages. After repeated use, a permanent discoloration develops which makes accurate reading increasingly difficult. This may be caused by the chemistry of the liquid or colored residue of the liquid which is absorbed by the dip stick. Also, during wet weather, the wood dip stick may become wet causing a discoloration which makes the wet to dry boundary on the dip stick difficult to see. Another disadvantage of currently used dip sticks is the necessity of waiting for the dip stick to dry before it can be used again. Such dip sticks therefore cannot be used to successively measure the amount of liquid in a number of tanks during a short time period. Also, since prior dip sticks generally rely upon the surface attraction between the wood material and the liquid, they are generally not as useful and accurate for measuring volumes of liquids where the surface attraction is low.
These and other disadvantages are overcome by the present invention. The dip stick of the present invention consists, in the preferred embodiment, of a long, cylindrical, transparent tube fixed in a longitudinal groove in the side of a strip of wood; the wood, except for the groove, having the composition, shape, size and calibrated height indicia of a conventional dip stick.
A portal (valve seat) at one end (the bottom) of the tube is opened and closed by plug-like valve piece which is suspended below the portal by a non-corrosive wire which passes through the tube to an opening at the top of the tube. Means for pulling upward on the wire to lift the valve piece and seal the bottom portal is provided at the top opening. A leverage handle is suitably mounted to the top of the wood strip for this purpose. A contraction spring mounted to the bottom of the tube biases the valve piece away from the bottom portal to keep the bottom portal open except when the valve piece lifting means is actuated. The transparent tube is suitably composed of cellulose acetate butyrate which is impervious to gasoline and unaffected by hydrostatic pressure at depths of up to 15 feet.
The dip stick tube of the present invention provides a simple and convenient way to more accurately measure the volume of liquid in a container irrespective of weather conditions. The present invention also has the advantage of being able to accurately measure the volume of any liquid which does not cause the dip stick materials to deteriorate. The accuracy with which the present invention may measure liquid volume is not inhibited to a low surface attraction between the tube and the liquid as is the accuracy of conventional dip sticks.